Category Archives: Evolutionary Biology

Lasers lock X-ray beams onto the remains of Clarisse, a 50-million-year-old snake. The fossil was scanned on a 64-slice CT scanner at The Methodist Hospital in Houston, and the resulting images were analyzed by Brazilian paleontologist Hussan Zaher. The snake is part of the collection at the Houston Museum of Natural Science and will go on display in 2012. (Credit: Photo by Denny Angelle/The Methodist Hospital System)

ScienceDaily (Sep. 20, 2010) — Even some of the most advanced technology in medicine couldn’t get Clarisse to give up all of her secrets. After all, she’s protected them for more than 50 million years.

Clarisse is a snake, found in the Fossil Butte region of Wyoming, perfectly fossilized in limestone and the only one of her kind known to be in existence. Palentologist Hussan Zaher came to Houston at the behest of the Museum of Natural Science to study her.

He brought the precious find to The Methodist Hospital and subjected her to a detailed CT (computerized tomography) scan in hopes of finding where Clarisse fits along the timeline of evolution.

“Most fossilized remains of snakes are individual pieces of bone,” said Zaher. “This is unique because it’s a complete snake, which gives us an opportunity to study her makeup and hopefully learn more about her.”

CT scan technician Pam Mager conducted the scan on a 64-slice scanner that is capable of sending laser-guided X-rays through a target. “We can take almost 3,000 images in less than a minute,” she explained, “and then we can use those images to construct a three-dimensional picture of the snake’s bone structure.”

Zaher, professor and curator of the collections of herpetology and paleontology at the Museu de Zoologia of the Universidade de São Paulo in Brazil, worked with the Museum of Natural Science in Houston to get Clarisse to Methodist for the scan. He believes Clarisse could be an evolutionary link between snakes who take a lot of small bites to eat their prey and snakes who swallow their prey whole.

The snake fossil was preserved in what is now limestone, and the entire chunk of rock was placed on the bed of the CT scanner. In less than a minute, the images were taken and assembled by computer into a three-dimensional image that could be rotated 360 degrees.

Taking a preliminary look at the images, Zaher said he saw no traces of limbs. “That places it higher up the evolutionary scale, but the snake is still very old,” he said. For more than an hour, he and technician Mager studied the images, looking at tiny details of the snake’s skull to find clues to how it may have eaten its prey.

Clarisse is the best preserved Caenozoic snake known in a U.S. scientific collection. According to preliminary analysis, this snake is believed to be closely related to Boavus indelmani, a booid snake described in the late 1930′s. Zaher and the Houston museum hoped that getting a look at the underside of this unique fossil, as well as the inside of bones like the skull would shed some light on the evolutionary history of the species, and its relationship to booid snakes (like pythons and boas).

“This is a very important step in studying this specimen … I will be able to take away copies of the images for further investigation and I believe this will help us learn about this snake,” Zaher said. “I cannot express my gratitude enough to (The Methodist Hospital) and the radiology services department here.”

The snake is part of the collection at the Houston Museum of Natural Science.

Erik Svensson conducts research on damselflies. He has shown that enemy-victim relationships can also occur within the same species. (Credit: Erik Svensson)

ScienceDaily (Mar. 19, 2010) — Stay and fight, or flee? These are usually the alternatives facing a victim when it is attacked by an enemy. Two researchers from Lund University have now collected and discussed various examples from the animal world where the victim makes use of another possibility.

“The victim can allow the enemy to remain and instead try to live with the consequences,” explains Erik Svensson, Professor of Animal Ecology at Lund University.

There are many examples of ‘coevolution’, i.e. where the enemy and the victim influence each other’s development in close interaction. In several plant studies it is for instance a relationship between a parasite (the enemy) and its host plant (the victim). Erik Svensson and his colleague Lars Råberg have recently published an article in the journal Trends in Ecology & Evolution, in which they discuss the evolution of enemy-victim relations in animals.

The cuckoo’s brood parasitism is a classic example. The great spotted cuckoo lays its eggs in the nest of the European magpie and lets the magpie pair raise its young. The magpie can in turn respond by trying to recognise alien eggs and reject them; this is a form of resistance. However, there is a risk that the magpie may accidentally reject one of its own eggs. In addition, the magpies that reject cuckoos’ eggs run a higher risk of having their nests destroyed by adult cuckoos. There is evidence that magpies that live in close proximity to great spotted cuckoos actually compensate for this by laying more eggs than magpies that breed in areas where cuckoos are not present. One reason for this could be that it is a way to compensate for the eggs that risk being destroyed. This defence tactic is classified as tolerance, rather than resistance. It means that the victim tries to live with the presence of the enemy instead of resisting.

Erik Svensson conducts research on damselflies. He has shown that enemy-victim relationships can also occur within the same species. When damselflies mate, the male clasps the female’s thorax. Immediately after fertilisation, the female begins laying eggs. Yet females are constantly subject to mating attempts and harassment from other males, which incur costs in the form of a reduced number of eggs. However, some females have developed a higher tolerance to this mating harassment, which means that they are able to partly buffer the negative effects of mating harassment on their egg laying.

Lars Råberg has studied tolerance in mice. He has performed an experiment in which he infected different mouse strains with malaria. It was apparent that the different mice did not become ill to the same extent, despite the fact that they had the same number of parasites in their bodies. Thus tolerance can also reflect itself in how sensitive a victim is to an enemy.

“This is a new way of viewing the evolution of enemy-victim interactions in animals. The role of tolerance in such interactions have previously been discussed primarily in the context of the plant world. We believe that tolerance could be at least as important as resistance in animal co-evolution between enemies and their victims,” says Erik Svensson.